Well... whoever expected that a Brexit would not lead to economical war of secession with the EU must have been quite deluded. It is perfectly clear that the rump-EU will now do everything in their power to show to other possible separatists what will happen if you actually do. Britain will be economically isolated as much as the EU can manage lest they are willing to pay the tremendous separation charges which are part of the warfare Brussels is waging.
On the other hand, Britain's hands are not totally bound in this. The EU should not forget that they need the British airspace for their daily NATL business, so what if Britan would unilaterally bring on large overflight charges for EU carriers just for starters? Or deny overflight? There are many ways an independent nation can make things very awkward and expensive for unfriendly nations who still need to do some business. Britain has chosen this way and now it is the time to see it through, not to wonder how to migate side effects. Being outside EASA might actually be a profitable business at the expense of current save havens like the Isle of Man, Channel Islands or San Marino... and working in the direction of closer cooperation or adaption of ruling towards the FAA might make a lot of people happier than in the current state.